Collective data on the treatment of sewage by the activated sludge process

TKEAT/nENT OP SEWAGE BY THE

A. A. HAMAEK/^AN

ARAOUR INSTITUTE OF TECHNOLOGY

19 2 0

628.3
H17

•i- ■<:■ •■ : '

of Tecliaoiogy
UNIVERSITY LIBRARIES

AT 539

Hammerman, M. A.
Collective data on the
treatment of sewage by the

For Us8 In Ukary Only

I ; V U in ( (I U I
[IN, /. I, S

( (■ I ' ,' f ' ' ^

Collective Data on the Treatment of Sewag,e
by the Activated Sludge Process

A THESIS

PRESENTED BY

Meyer A. Hammerinan

TO THE

PRESIDENT AND FACULTY

OF

ARMOUR INSTITUTE OF TECHNOLOGY

FOR THE DEGREE OF

Bachelor of Science

IN

CIVIL ENGINEERING
May 1920

ILUNOIS INSTITUTE OF TECHNOLO
PAUL V. GALVIN LIBRARY
35 WEST 33RD STREET
CHICAGO, IL 60616

[jj DEAN OF ENGINEERING STUD

DEAN OF CULTURAL STUDIES

I. r ( i-

TASLE QdP CClTTICvTTS
Bibliograplij'"

Acknowledgement

Introduction

Experiments Leadin;^; To Dis-

coveiy

Early Exijerimenta
Experiaasnts At lilancliester

Experiments in The United

States

Llilwalkee ExxDeriments

The Sludge And Its Disposal

Graphs

page

I'

V

2

n

5

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9

ft

II

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I6

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22

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^9113

Digitized by tine Internet Arciiive

in 2009 witii funding from

CARLI: Consortium of Academic and Researcii Libraries in Illinois

http://www.archive.org/details/collectivedataonOOhamm

Biblioiiraploi'-
Engineering & Contracting
Engineering <2c Contracting
Enginesrini; ^ Contraotihii
En^ineerinji & Contracting
Engineering &; Contracting
Engineering & Contracting
■3ngin»ering ic Contracting,
Eng ine e ring ?Te vvs
Engine erihg ITews
Engineering Ivews
Engineering ITews

Engineering ITews
Engineering ITev/s

"Engineering ITews-HecoSA^

Engineering Record

Engineering Record

Municipal Journal

Oct.

P7

1915

Tsc,

1,

19 15

PeiD,

2,

1916

liar.

1916

Ai^r.

26,

1916

xTov .

8,

1916

Jul.

51,

1918

Apr.

j^.

19 15

Jul.

15.

19 15

Jul.

29,

19 15

Pec.

2 ,

1915

Oct.

12,

19 1 6

17ov-

25.

19 1 6

ITOT ,

I,

19 17

Apr.

5,

19 15

Oct.

^16,

19 15

Pe"b.

10,

19 1 6

I t^!k« this opportunity of expressing m/
appreciation to Professor John C. Psnn for
suggesting tliis sutject and to Miss A. E.
Pisher, librarian, whos« assistance in the
literary was a jcreat help to me in preparing
this thesis.

-I-

Introduction
until recently the medical profession has
been the sole guardian of the public's health.
The system it uses is to prescribe a cure for

a disease, but it does not seek to prevent it.
The engineering profession however, lead by the
sanitary engineer, is supplanting to a certain
extent the doctor and his medicine. A typical
case is the fall in the death rate due to ty-
phoid fever. This was accoiirplished by sanitary
methods of treating drinking v/ater. Other cases
involve the disposal or treatment of sewage.
The best, cheapest and most efficient method
of attaining this end is a matter of much dis-
cussion. One method which has been devised re-
cently is the treatment by the "Activated Sludge
process".

The writer has chosen this as his subject,
because of its infancy and great future. The
day will soon come when every city and town
will have a sewage disposal plant that gives a
profit and is not a deficit to the operators.

-31-

Experinients Leading; to Discovery.

The method of treating seaage 'o'j the ac-
tivated sluge rjrocess was first formulated
oy Po'<7ler and iiuciford, who were conducting
experiments on sewage in Lianchesterj Eng, ,
in 1915» They were investigating; the action
of an organism which they designated as lij ,
Thej/ found that, if this or_ anism was cont'.'/i':'ed
in sewage, the sevrage was clarified after 6
hours of aeration and that the effluent was
non- putrefactive. This sluce -olayed an impor-
tant part in the results obtained, as it was
noticed that if the sewa^^-e samples were aar..;-
bed continuously for 5 weeks, complete nitri-
fication '.vas ohtained, Twlien more samples wero^
to he tested, the clarified sewage was drawn
off and the nev/ sample w.-..s used .vith the old
sludge. The time for oxidation v/as reduced tc
24 hours after a number of samples were clari-
fied without removing the sludge,

T^nese experiments were "brou'ht about in

-S -

order to find a cheaijer and raoxe satisfactory
method of treating sewafee. It was known that
the most costly part of modern sew?.ge works,
including the ca,pital expenditure and often
the revenue charges, was the filtration area
The area and cost of filter beds depends naainly,
it was found, on the amount of colloidal matter
present in the sewage and much confusion of
ideas was due to the fact that the ordinary
sewage filter, "be it contact or trickling, Jras
called upon to do t'.ro entirely different things

aj the same time^for it to oxidise, granulate
ar.d finally discharge as humus the colloidal
uatters present and second to oiidize and nit-
rify substances in true solution. It w-s also
rhovm that a tank effluent, well clarified Tpy
sedimentation could, by accurate distribution
be very efficiently purified on filters of fin^;

;ra,terial, but even then the area and cost in-
Ijolved in exceptionally large works, made the
problem a verv serious one.'

-4-

For these and of.-.er Tez.zons the thoughte
of niany v.'-orlcers in serrar:e treatment ivere turned

to the poEsitility of a more efficient re-
i"oval of the collodial matter before the fi3^
tration process.

Sefore this process was evolved ^only pr:;x-
tical method was oy heavj' chemical precipit:a-
tion. The cost cf operating a plant vThere'by
the collodial matter was removed "by the addi-
tion of a chemical to the sewage was very hi _;.h
and was money thrown a^vay. It '^as not only t'xe
cost of the enormous quantities of chemdcals
necessary, hut the removal of the vast amount,
of resultant sludre that "became increasingly
difficult and costly.

Messrs. Fowler and TJIumford sought to find
a method of obtaining a thoroughly clarified
efficient -dthout the use of large quantities
of chemicals and with the minimum production
of sludge. By a thoroughly cl:,rif3ed §-iflmnV:
is mea.nt one ':frAcla wi 3 1 not eventually depos-

-5-

solid matter either on the "oottora of a stream
into \f;hich it flows or in the interstices cf
a bacterial filter,

Mr. Murriford in the coarse of research in
another riutter had the occasion to study tlie
the action of an organism occuring in nature,
in pit '.vater impregnated with iron. This or-
ganism-which for convenisnce has 'been desig-
nated as W/ is a true facultative organism,
preferably an aerobe, and exercises a specific
action on iron solutions. It was found that this
hacillus precipitated ferric hydroxide from
iron solutions and in order to precipitate the
iron sufficiently the organism required a cer-
tain proportion of alhuminoid orr.anic matter.
It was therefore natural that ordinaiy sewage
r;hen acted upon "b}'- this organism could he util-
ised in this -vaj;. Experiments, in fact, showed
that a sewage effluent could be effectively
clarified in this u'-ay when acted upon by this
.or/;:anism in the presence of si/w 1 Quantities

-6-

^, «*>'*

of ferric ycilts, a,na tierobic ooriviitions l/eiiie
iTiaintained in tlie liquid 'b;'- means of a current
of air. The process requires therefore that t'.e
grosser solids should be removed Toy sedimenta-
tion so ciS to have the least a,mount of putre-
factive mt?,terials in the liquid portion of the
s 6 rra^c e •

The ordinary methods of sewage analyris
fails to reveal the change which has really
taken t^lace during this process, as they do
not differentiate "betv^een organic nitrogen-
ous material, in the colloidal and cr^T-stal-
lojdal states respectively.

-8-

r.ai:ly Experiments.

Experiments in tlie laboratoiy were iriide v.-itli
the conditions during the process maintained as

far as possible aerobic throughout, and there
being always a certain amount of ferric liydrc.te
j::re£ent to oxidize offensive sulfer compounds
o.nd no offensive odor v/as produced.

By this method a liiiiped sparkling and non~
,-utrifactive effjuent was obtained from domes-
tic sev/age dravvTi from a sewer near the labora-
toiy, Experiments indicated that one gram of
iron- salt per f-allcn ^as the maximum need and
that a total of twelve hours tankage, i.e. six
liours aeration and six hours settlement, was
sufficient.

Another feature found out w-s that once the
; ro'wth of or.r-anisms liad been established in tJie
tank, there appeared no difficulty in maintain-
ing it. The one hindering feature however, was
file cost of air blast; the pressure of air ho'.7-
ever, depended eimply on the dejjth of •iV:^ter to

-9-

Toe Tolown through and a numliex of , _ ' ^-'eerin--
conditions ^vould naturally affect part of 'lis
protlem.

The advance claimedj is the use of a spe-
cific orgciinism found in nature, together
with iron salts, to affect the clj^rif icaticn
of the effluent, that is, the coagulation of
the colloidal nritter as distinct from the .ur-
ifi cation of the effluent taken an a whole. To
use a simple illustration the addition of .
little rennet does not appreciahHy alter t^ie
contents of milk as a whole, "but separates it
into a solid and liquid portion. The endeavor
of tlie discoverers was to obtain a similar re-
sult in the case of seva-e tank effluent.

-10-

Experiments at Llanchester.
Purther experdnients were carried out on
this line "by Messrs. Arden cz Lockett in 1914-
at jvlancli ester. Tlie sanTnles consisted of 80 oz,
cottles of I'ilanchester raw sewage. They were a.^r-
-vted until complete nitrification, h\'' dra^;ing
_,ir through the sewage "by means of an orddnar;/
filter pump. For the first sample five weeks -:s
required for com";lete nitricication, after •" '.ch
t]'ie clear liquid was dravv-n off and another s:;. ^le
of 80 oz. added to the bottle containing the set-
tled sludge and this again aerated until complete
nitrification. This method of treatment vras re-
peated severa] times .vith retention in each c,:.i-ie
of the deriosited solids.

It w-s found that the amount of solids in-
creased and the time required for each success-
ive aerating- deminished until it ivas possihle
to oxidize a fresh sample within twenty- four

:ars. The experimenters ca.] led these deposited
r^clids ""ictivatea sj-uogei*

-II-

\^ith tliisc activated siud;"e a further se-
ries of samples '^ere tested. In general a pro-
vortion of one Tolurne of activated sludge to
four volumes of s enrage of tiie ■jreceeding ex-
periment much smaller proportions were used.

rrom these tests the following.- conclu3i(r;i3
■vere ms.de, tha-t an extraordinary high degree
of x->urif ication can "os obtained ;vithin a rei'-
sonahle period of time by aeration in contact
'.vith the activated sludge. The amount of ni-.
trificition dependih;^; to a certain extent on
the concentration or strength of the sewage
dealt with. On the averajje, aeration under tlte
conditions of the experiment for a period of

ix hours, with subsequent settlement, was suf-
-"icient to obtain a high percenta£;e of pmri-
fication. In all cases the resultant effluent
"as non-putrefactive on incubation. .

These experiments were 'vorked on the dra-
md fill method and. it 'vas anticipated that
equally f-ood results could be obtained by vvor^li-
in.^ on a continuous flow basis.

-12-

Further experiments in tiiis line showed
that the activity of the sludge is gradually
diminished, when working on the fill and draw
method, if it is called upon to treat futher
samples of crude sewage, prior to the complete
nitrification of the previous samples dealt with.
The results also showed that this difficulty
would be overcome by simple aeration of the
sludge alone, until the free or saline ammonia
content was removed.

Experiments were then carried on to deter-
mine the influence of temperature on the oxida-
tion, prom these experiments it was found that
the oxidation process could be maintained with-
in a fairly wide range of temperature. The ex-
periments carried on for temperature less than
10 C showed that an inactive sludge was produced.
With a temperature of 30°C it was found that the
initial clarification effect was to some extent
interfered with and that the effluent resulting
from subsequent settlement showed a slight deter-
ioration, ,

-13-

Activated sludge aocumulated in this raadAer
as descri'bed 'oy the investisators is "quite
inoffensive, dark Taown in color, and flocculent
in character, and despite its low specific grav-
ity separates from v;ater or sewage at a rapid
rate. After prolonged settlement the activated
sludge, however, rarely contains less than 95
per cent, of water, A remarkahle separation of
the water from the sludge can he readily obtain-
ed "by treatment of find grade strainers, with
the production of a sludge of the consistancy
of a stiff jelly. Gelatine counts have shown a
bacterial content of at least thirty million or-
ganisms per cubic centimeter. In addition, the
sludge, hy reason of its nitrifying power, must
of necessity contain a large numher of nit±lfy-
ing organisms. It should also "be noted that a
fairly large nura"ber of protozoa were found".
It does not, however, contain any algae growths.
The chemical analysis of an average sample of
activated sludge is as follows :-

-14-

Organic Katter 64.7 Per cent

Mineral " 35.3 " "

Total nitrogen (n) 4.6 " "

Phosphate (PS 05) 2.6 " «

Matter extracted "by
CarlDon Tetrachloid CGL4 5.8 " "

Attention should 'be called to the ahnorcially
high percentage of nitrogen as compared with
ordinary unoxidised sewage sludge.

Experiments 77ere carried out in the open, as
compared v;ith the previous experiments which \7ere
performed in a laboratory and the same results ob-
tained. An air diffuser was also uded instead of an
air tube and the results showed and increase in the
oxidation of sewage. A continuous system of flow
was also tried and the result was that the amount
of ammonia present in the effluent increase'd as
the experiment proceeded and rendered it necessa-
ry to recirculate the effluent through the aera-
tion tank again. Prom this it was seen that the
sewage must flow very slowly through nine series
of aeration tanks in order to properly purify

-15-

the sewage,

-■■ ■ !

I

Experiments in U.S.
Similar experiments of this sort were con-
ducted in America at Urbana, 111, in TsToTrem'ber
1914 and then tn a large scale in May 1915 by
Edward Bartow and 5',W,Mohlman of the State Y/ater
Survey, University of Illinois, The first exper-
iments were made on raw sewage without activated
sludge present and the results showed that com-
plete nitrification could be obtained within the
limits of 15to33 days by blowing air into the sam-
ple by way of a tube. They then used an air diffu-
ser with a similar sample of sewage and complete
nitrification accured within 15 days. In each
case the faee ammonia nitrogen was oxidized to
nitrite nitrogen and further oxidised to nitrate
nitrogen. It took 4830 cuft of air in the second
case for the forsiation of the nitrate. At the end
of seven days the free ammonia nitrogen was com-
pletely changed to nitrite ni tro gen , slowly changed
to nitrate nitrogen.

-16-

When a similar sample was examined in the
presence of activated sludge complet nitrifica-
tion "was accomplished in five days and the amoimt
of air used "was only 1270 cu. ft. The supernatant
liquid was then drawn off and another sample added
to this accumulated sludge and aeration continued.
In this treatment complete nitrification took
place in two days with the use of hut 720 cu.ft.
of air. Treatments 7;ere continued, al-ways de-
canting off the clear liquid and a new sample
added to the sludge accumulated until the twelfth
treatment, when theresults shov?ed complete nitri-
fication in less than eight hours with the use of
only 128 cu. ft. In the thirty-first treatment
there had already settled enough sludge that the
proportion of sewage to sludge was five parts to
one part. Por this sample purification was oh-
tained in less than five hours using 35 cu, ft,
of air, this heing ahout 3 cu.ft, per gallon of
sewage,

samples taken every hour of the sewage, in
the operation of the last experiment named, showed

-17-

■) -;j/

M :. n 1 I , \ rr\-c I I I \

At Uji i _

that the free ammonia is not chagged to nitrite

and the nitrite oxidised to nitrate but that ni-
trates and nitrites were formed simultaneously.

Biological examinations then made in the
sludge showed the presence of a slender v/orm
whose lenght varied from two to five ram. It is
known to abound in fresh water bodies where there
is an abundance of decaying organic matter and
thrtves especially where there is much fermen-
tation and in waters contaminated with sewage
providing there is an abundance of oxygen. These
worms probably destroy at least their own weight
of organic matter each day. Because of their re-
production by fission extensive colonies can be
produced within a short period.

These worms, no doubtedly are the main con-
tent of activated sludge. The sludge does not
have an unpleasing odor, owing to the fact that
it consists largely of living organisms. If kept
for a long time in a moist condition without air
i t will piitfcfy. The chemical analysis of this
sludge after drying first on a water bath, then
for three hours in an oven at lOO^C the loss of

-18-

t^

moisture Tseing 95,54 j\er cent» was:-

lTitrogen(N) 6,3 Per cent,

phosphorous (p I 1,44 " "

phosphate(^P^05) 3.31 ", "

Pat 4,00 " "

Volatile matter lost
by ignition 75.00 " "

The percentage of nitrogen and Phosphate
are higher in this sludge than that obtained
at Manchester,

Eurther experiments v;ere made at Urbana
in May 1915, These experiments "were conducted
in four large concrete tanl:s each having an
aeea of 10 sq.ft. and 8ft. 5in. depth above
X^ in. filtros plates which were used to dif-
£use the air. In two tanks, hine plates were
used with spaces of one inch betv;een them and
in the third tank there were three plates cov-
ering one- third the area of the floor with a
central tl'ough sloping to the plates at an an-
gle of 450, Jn tiij fourth tank one plate was used
in the center covering one ninth the area of the

-19-

floor and 7a th the bottom sloping to it at
an angle of 45° on all sides. Below the plates
was an air space of four inches deep. These tanls
could "be filled in six minutes and drained in
eight minutes, through two outlets which are re-
spectively 2» 6" and 5' 7" alROVe the porous plates.
Uo iludge was lost through the outlets of the
third tank "because movable outlets were used. TJie
first and second tanks were filled with the same
kind of sewage, the sewage in the first tank be-
ing aerated continuously, and in the second tank
for 23 hours, the sludge b44ng allowed to settle
and the supernatant liquid drawn off and one hour
later more sewage added to the collected sludge.
This cycle was repeated daily and results were
recorded. After ten days one per cent of volume
in the first tank was sludge and in the second
tank 10^, The effluent from the second tank was
clearer than that of the first tank. The opera-
tion of the second tank was continued as before
and after 15 days, nitrification was complete.

-20-

The sewage was then changed every twelve hours
and nitrification was complete in eight days.
Changing the sev.'age every six hours did not show
good results and it "was necessary to aerate for
longer periods. This comparison indicates, how-
ever, that sludge may be satisfactorily activa-
ted by changing the sev.'age before nitrification
is completed and that the sewage may be changed
at frequent intervals. The third tank give stable
effluents after five days. The fourth tank did
not give stable effluents in 18 days*^

Further experiments at Jlrbana with activated
sludge took place in 1916 with continuous opera-
tion and results showed that 90^ of the suspended-
matter was removed and after 13 days of operation
stable effluents were obtained.

-21-

MilwauJ^ee Experiments,
Further experiments v-ere carried out "by
T. Challcley Hatton* chifif Engineer, llilwaukee
Sewage Commission at Milwaukee since 1914, The
magnitude of these experiments Taeing larger than
those at Urbana, Experiments were carried out
in liTarch 1914 one a small scale so as to get an
idea as to the plant necessary to experiment on
a larger scale, Tww glass tubes 6' long "by 1^^'
in diameter were used. Air was forced into one
of these tubes through filtros plates and an-
other through a tube. Results showed that after
24 hours aeration in each tube the nitrification
in each of the tubes was about the same, A tank
of Isrger capacity was then built outside. This
tank measured 32 ♦ lone 108 6" wide and 10 » deep,
piltros plates were set at the bottom of this
tank and the effluent drawn off by means of a
floating circular weir. This tank was operated
under varying conditions. The results for nor-
mal conditions being, filling one hour, aerat-
ing three and one-half hours, settling one-half

and drav/ing one hour, Further experiments were
carried on in a tank 10 ft. hi^ 5 ft wide, one
foot between sides. Glass plates were inserted
at various depths to observe the action inside.
The results obtained from -/this experimental tank
showed a greater number of bacteria per c .c, for
the filteos tank than for the iit . ■ Jet diffuser
tank.Sxperiments were then conducted on continu-
ous flow operation. The tank being of the same
size as the one used in the second set of exper-
iments. This tank was put into oeration after
securing the activated sludge. Experiments were
carried out with varying Trolumes of air per gal-
lon of sewage treated, varying rate of flow and
varying the volume of activated sludge. The re-
sults for this tank are as follows, the larger
percentage of the sludge in the tank, the more
nearly complete nitrification is obtained, that
is, for percentages of sludge up to 12-g^ for vol-
ume.

All of the preceeding esflperiments were car-

-23-

%'.'.^'

ried out in relatively warm weather, so the
question came up as to hov; the process .vould
work in cold weather, as the "bacteria did their
test work in tezaperatures between 689 to 70°P
Tests were made on the liilwauicee Sewage in Win-
ter the temperature of the Sewage ranging from
55°p to 420p and it occasionally dropped down
to 4oO These ?ery low temperature, re tar ted the
oxidation of the organic matter and decreased the
staTaility of the treated liquid. Activitjfng this
sewage with 2^ cu, ft. of air per gallon, 90
per cent of bacteria in the se;vage was removed
and the suspended matter reduced to about 15
parts per million.

By increasing the ipolume of air applied
■ the plants could remove the suspended and col-
loidal matter and bacteria in a satisfactory
manner. As the temperature of the sewage dropped
the oxidation of the organic matter decreased
the nitrates in the effluent falling more than
100 per cent for a difference of temperatures

-24-

of 63*^ to 49° 3-^^ the oxygen consumed "was in-
creased 75^. Tlie decrease in oxidation was al-
so accompanied ^by a decrease in the stability
of the effluent. In cold weather the treated
liquid contained a large percentage of dissol-
ved o:xygen and only a trace of nitrate, where-
as in suminer the nitrates were high and the dis-
solved o:jcygen low. This shows that the liquid
seems to depend upon nitrates in summer and
dissolved oxygen in winter for its stability.
This shows that in winter temperature, good
"bacterial removal and ci.arification can "be
aiaintained without oxidising the ammonical
nitrogen to nitrate.

These, and the proceeding Kil*aukee exper-
iments proved that it was possible to treat the
sewage of Milwaukee by the activated sludge pro-
cess on the continuous flow method when the tem^
perature of the sewage was 50°P or over at less
cost than by any other process. It was then de-
cided to build a plant having a capacity of
1,600,000 gallons a day. The estimated cost of

-25-

the plant was ^65,000 "but the plant -was complete^
in January 1916 at a total cost of but $61,536 in-
cluding all machinery and cost of engineering and
inspecting.

The activated sludge plant is Ideated on Jones
Island, alongside a large outfall sewer of the com-
bined system. It consists of eleven cylindrical, so
that if the activated sludge process should fail
they could be easily converted into Iichoff tanks.
Of the elven tanks, eight used in series are used
for aeration of the selvage in the presence of ac-
tivated sludge, one is a sedimentation tank and two
are sludge, aecation tanks. The sise of the tanks
are as follows, they are all 30* in diameter and
have side walls extending 13 ♦ above its inner bot-
tom. The total depth of sewage and sludge is 10*
and the average depth is 9' in the ten tanks used
for aeration. The sewage and the sludge in the sed-
imentation tank is 35, 2» deep. The holding capacity
of Aach of the eight sewage aeration tanks is 45000
gallons or 360,000 for the group. The open area of

-26-

© ,■

6ach of these tanks is 662,84 sq, Pt, and all
4f them 5,303 sq. ft. The sedimentation tank
has a holding capacity of 33, 000 gallons,
not including 2,260 gallons held Toy the 48"
cast iron sludge pipe extending "below its bot-
tom.

The general scheme of operation is as
follo"ws: the sewage is admitted to tank 1
where it is aerated with activated sludge, it
then passes succession through the first
eight tanks the combined sewage and sludge
passing on from one tank to another and then
into the sedimentation tank 9. Here the sludge
settlement and the clear liquid passes out in-
to the lake, Prom the bottom of the deep well
in tank 9 the sludge is discharged by gravity
into either of the sludge aeration tanks 10 or
11, The aerated sludge from these tv.'o tanks
passes outside the tanks to a 48" vertical cast
iron pipe set 28^« in the ground from which it
is lifted by air and returned to the inlet to
the sewage-aeration tank 1,

-27-

Tlie portion of the activated sludge in ex-
cess of what is necessary to maintain the proper
percentage in the aerating tanlca. is pumped out
of the sludge tanks from time to time and de-
watered and sold as fertiliser.

The normal lake level is at El, -1.4. Tlie
sevjage level in tank 1 is El,-V 0.8 and the
weir in the sedimentation tank is at El. ^ 0.5
giving a fall of 3» in water level through the
series of tanks.

By means of the curved baffle or division
wall: the sewage travels and is subjected to
aeration for a distance of 912». Air diffusion
affected "by means of 12 x 12 in. filtros plates
781n each sewage and sludge aeration tank. This
gives a ratio of diffusing surface to tank sur-
face of 1 to 8.5. Tlie filtros plates are set in
aast iron frames, which afford an air supply con-
duit beneath the center line of each plate . The
estimated air capacity of the filtros plates in
the eight sewage aerating tanks is 2 cu. ft. per
minute and in the tv.'o sludge aeracing tanKs it is

-28-

12 cu.it. in ecion c^se unaer u, 2 in. ^c^ter
pyeseure.

This plant was designed to treat 1, 600,(X)0
gallons of sevrsige per djy with a four hours es..

iod of aeration and with 25 pe^: cent activated
sludge content, a velocity of 3.8 ' per min.
and 27 min. sedimentation petiod. It can also
Toe run with 25 P^i" cent activated sludge pres-
ent running through at a velocity of 5 ^"t* "02:
5 hours and a 20 Eiin. sedimentation period, the
capacity for this operation "being 2,160,000 gal-
lons, A capacity of 2,304,000 gallons daily is
ohtained .vith 20fS activated sludge running through
at a velocity of 5 ^t. per min. for 3 hours and
a $SL 19 minute sedimentation period.

The results drawn from this plant after a
year of continuous operation are numerous, and
man;,'- new experiments were tried there, but on a
larger scale, and their results obtained.

mien this plant was first put into operal^i^n
it required from 30 to 55 claj'-s of aeration to
o"btain a sufficient cuantity of activated slud^

-29-

30 as to start work, and in order to niaintain
25 per cent of activated slud£:e in the aerating
tanks it had "been found necessary to return frora
the sedimentation tank from 40 to ^0 per cent of
the voluire of raw liquor treated, hecajjaea the Li-
quor drav.Ti from the sedimentation tank was only
about one-half sludge.

Tests for this best diffusers to use v;ere
also made. It was found that the filtros diffu-
sers created too much frictional Iobs, the loss
being three- fourths'^f or forcing a five'^-air pres-
sure through. Tests v/ere made with wood block
cut from basswbod across the grain and the fric-
tional loss for these filters were only oneOhalf
pound for five pound air pressure. The wood fil-
tros plates are cheaper and nitrification V7ith
less air could be secured by increasing the dif-
fuser area about 3^fo over air required for fil-
tros, and thus reducing the volume of air pas«-
ing through each square foot of diffuser.

The aerating tank which gave the best re-

-30-

suits in luilwaukee has the following proportions:
1 sq. ft. of diffusing surface to 5-5 sq. ft. of'
tank surface, average depth of liquor, 9 ^t. 275
gallons of rav; sewage treated per day per sq, ft.
of surface. One culDic foot of aerating tank ca-
pacity treats 29 gallons of sewage per day.

The results obtained from the sedimentation
tank at this plant were not very good, the Elua,:e
could not lina its wd^'- dov/n the central well and
therefore collected on the sloping iDottom of the
tank and the sludge became septic. This settling
in this manner v;as due to an entrance velocity
which -^.s too great and adverse currents were
established which held the finer flock in sus-
pension, permitting it to pass over the wtn
with the effluent; the heavier sludge v/ould
settle or the sloping bottom and not slide down
to the central well and it became septic there,
Prom further experiments conducted it was found
that the tank giving the best Sedimentation was
a tank ,7110 se ratio of -^he breath to the len^JtCti

-31-

m^ lii^'i'w

was as 1 to 2.3 with flow across the breath.
The running velocity should not exceed 3 ft.
horizontal per minute. The detention period
may Toe i'rom 30 to ^0 minutes, according to
the character of the selvage treated. Vertical-
horizontal flow heing more efficient than
either vertical or horizontal flow. The eff3.u-
ent should he removed with the least Velocity
Tjossihle and over Continuous rather than V
shaped weirs the latter creating cross cur-
rent just where they are most ohjecitional.

-32-

Tlie Sludge and Its Disposal.'
After ti'id sludge ccllects into the sedi-
/iientation tank it is rei.-oved, aevntatered, pre-Soed
.-nd sold ae fertiliser. The fertilizer "being
^,old for ^12.50 per dry ton in 1937, Tlie cost
liowever, of pressing and di^'^ing; the sludge v.-_. ich
Included inter^r^.t charges and plant deprecii-.tion,
lalDor and iraterials vvas ahout. $8.75 per dry ton.
The clear profit bein ^5.75 per ton. An analysis
of the sludge ohtj^ined is as follows:
Nitrogen ^.lf= as 1^5

rat 5.3^

« Soluble Phos-
phor i c ac i d 9 . 5/'V

Potash ,2^'ji

The value of the sludge depends upon sev-
eral things among v.-hi oh may be v/entioned the
percentage of availa'ole nitrogen and the quan-
tity of fatly liiatter it contains. The nT-;htr
the nitrogen content, the more vailuaV.le is the
sludge for nianure, but on the otlaer hand, the
hi^^her the fatly content the less &uitc*Gxpi is

-33-

J- "

ti'ie oiuci^e lor agricultural use until the i.^.t-
Ler inateria,! has "been reixoved. Ho'vvever, the
rore f-ot present, tlie more advisable it is to
i-i-eat the £lud:.e to recover this fat, if it is
_. resent in consiaera'ble quantities,

■Estirnating that one dr;" ton could he o"b-
tained from 1,000,000 gallons of sewage treat-
r-d. and an average daily dry v;eather flow of
'5><^00,000 gallons the nc-t cost of disposing
>!il',vaukee ' s sewage r/as estiinated at |9.64 per
1,000,000 j^allons of which 4-. 39 is charged to
overheads and ■;4-.75 "^'^ operating, uenewals, and
repairs. The net cost of operation per capita
is figured out to Ids ,53p»

But this Tfidy not Toe true, The actual valu-^
of sludge manure, depends upon the ease with
'.■/hich it can "be disposed of. Por small coiiunu-
•-ities surrounded hy rural districts fiere may
'ossilDly no trouTole -.vhatever of disposing of
this sludge at a payahlo ^.rice. !But v;hen a, rrr-i.-.t
osnter is considered, where great quantities of

-34-

< (

the sludge could "be xDroduCv...^, .^.,^/c is more t.-.an
can "be used by tlie surrounding farmers^! to ■; et
rid of it, uovld have to "be transported a £r;^at
distance and sold at :z cheapear price to make up
for 're transportation cost. Sewage sludg-c, ho-.vO
3rer .' high in available nitrogien is not BBch a
rich manure that it can stand the cost of hein^
carried half way across t'le \7orld like the chil~
ean nitrates. A comparatively small amount of
handling and carria^-e kills it as an article of
commerce.

Activated sludf;:e can he stored for a time
oeca-use there is no offensive oder to activated
sludge, but considerahle oiier mxay attend impioper
siudge reduction. Partially de'.vatered sludge, if
exposed to the sun for a few hours gives off a
. ighly oh.iectional odor of hydrogen sulfate. This
odor lasts for a short time only or until a .Iiy
cohering is formed. Suldge placed under cover and

not exposed to the sun ::^.ives off little or no
odor. Flies, insects s,nd '.vorms do not infest the

-S5-

- ©r:*fW^,

treatment plant, even during tlie early fall
vhcn tiiey are so prevalent in nearly all otl.sr
types of disposal plants.

-36-

a

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CODE

Curves^'-A- lVdl.'51we(ge +o SVol. Sewage

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